Browsers close within seconds, and the test suite holds up on a busy machine

Under load, Chrome's own shutdown could hang for about ten seconds, and every demo and browser check waited for it. Each browser now gets two seconds to close, then it is stopped and its throwaway profile removed. Installing the desktop app's shell is also faster, because a check for a still-running copy no longer looks up names of every network connection on the machine. With these fixes and a few longer test time limits, the full test suite passes repeatedly on a heavily loaded machine.